Typically, electrolytic capacitors have one or more active capacitance sections mounted in a metallic casing. Generally at least a portion of the space between the capacitor casing and the capacitance section(s) is filled with a potting compound in order to insulate and seperate the active capacitance section(s) from the casing and prevent vibratory movement of the capacitance section(s). Vibratory movement can cause mechanical failure of electrical connections internal to the capacitor and can damage insulation. The potting compounds typically used to prevent this vibration are a type of wax or pitch which can withstand some variation in capacitor operating temperature.
Several disadvantages have been found in this type of mounting. While potting compounds are generally satisfactory for capacitors used at moderate operating temperatures, they are unsatisfactory at high temperatures such as found in high voltage equipment and at low temperatures such as found in aircraft or spacecraft avionics. At high temperatures, potting compounds can melt and become dangerous fire hazards, since most potting compounds are highly inflammable. Further, interaction between the capacitor's electrolyte and the potting compound can cause deterioration of the capacitance sections and/or the potting compound over a period of time, which, in turn, can cause capacitor failure. At low temperatures, potting compounds can become brittle and ineffectual in restraining the capacitance sections. It should also be noted that potting compounds are messy to use and that if a capacitor casing is improperly filled the capacitor may operate poorly. Further, fumes from capacitor potting compounds can be hazardous to workers.
As a result of these disadvantages, alternate methods have been proposed for securing capacitance sections within a casing. In all of these methods, it is necessary to provide some kind of an arrangement which accomodates thermal expansion of the capacitance sections. Thus, it is not possible, for example, to provide a casing which tightly grips a capacitance section. As a result, various spacing and mounting devices have been proposed for insertion into the capacitor casing along with a capacitance section. Most of these proposed devices however, have not been widely adopted since they either greatly increase the cost of capacitor manufacture or are not wholly satisfactory in protecting capacitance sections from physical shocks and vibrations.
One example of such a device is disclosed in U.S. Pat. No. 2,758,259 to Peck, in which is described a supporting means for an electrolytic capacitance section. This supporting means comprises a preformed multilegged spacer with a central prong configured as a tapered cone to support the capacitance section. While this device is an alternative to the conventional potting techniques, the multilegged spacer is believed to be a relatively expensive device to manufacture; further since it only makes contact with the capacitance section at one location, it cannot fully support the capacitance section to effectively prevent vibration and other shock damage.
Another example of a spacing device for an electrolytic capacitor is shown in U.S. Pat. No. 4,459,641 to Giacomelo. In the Giacomelo device, a wrap-around support is positioned between a capacitance section and its casing. Although this device provides lateral (or radial) support for the capacitance section, use of the device adds an assembly step during the manufacture of the capacitor; that is, the support must be rolled around the capacitance section prior to its insertion into the casing. Further, it does not provide any longitudinal support for the end of the capacitance section.
It is an object of the present invention therefore, to provide an improved mounting spacer for capacitance sections in electrolytic capacitors.
It is also an object of this invention that this improved mounting spacer be able to protect the capacitance section from vibration and impact damage.
It is a further object of this invention to provide a mounting spacer which will be able to withstand extreme temperatures without losing its beneficial properties.
It is still another object of this invention to provide a mounting spacer for a capacitance section which is particularly suited for inexpensive manufacture and automatic insertion into a capacitor casing.